Eyesight testing devices for examining associated heterophoria of the eyes of a subject are known (for example, U.S. Pat. No. 5,331,358). The eyesight testing device described therein contains a first LCD display unit and a second LCD display unit. The first LCD display unit and the second LCD display unit are arranged one behind the other. The eyesight testing device contains a light source, which illuminates the LCD display units with transmitted light. On the light incidence side of one of each of the two display units, in each case a colour-neutral, see-through polarizer is arranged. The polarizers have polarization axes, which differ with respect to one another. In order to examine the eyes of a subject using the eyesight testing device, the subject wears polarized glasses, which have lenses with polarization directions which are different for the right and left eyes and in each case correspond, to the polarization axes of the polarizers. The displays on the first and second LCD display units are thus separated owing to the different polarization of light. As a result, if the subject's head is tilted to the side, the information displayed on the two LCD display units is no longer visualized in a clearly separated manner.